For the four circles M, N, O and P, following four equations are given: Circle M:x2+y2=1 Circle N¯:¯x2+y2-2x=0 Circle O:x2+y2-2x-2y+1=0 Circle P:x2+y2-2y=0If the centre of circle M is joined with centre of the circle N, further centre of circle N is joined with centre of the circle O, centre of circle O is joined with the centre of circle P and lastly, centre of circle P is joined with centre of circle M, then these lines form the sides of a :